1. Field of the Invention
The invention relates to a process for reproducibly producing uniform or non-uniform distributions of polymolecular association clusters, in particular, clusters of silver halide particles with photographic addenda. The invention further relates to apparatus for carrying out the process.
2. Information Disclosure
The distribution of photographically active chemicals among silver halide grains in a photographic emulsion significantly affects the sensitometric response of that batch of emulsion. Therefore it is important to be able to control this distribution to ensure batch to batch uniformity of the sensitometric response. An optimal distribution profile is a function of the photographically active chemicals, the emulsion of concern and the intended use. In some instances, it is desirable to have a non-uniform distribution of photographically active chemicals on silver halide particles to produce desired sensitometric effects such as a decrease in contrast. There is a need for a method to produce such a non-uniform distribution in a manner that is both controlled and reproducible from batch to batch.
This can perhaps be better appreciated by reference to FIGS. 1 and 2. FIG. 1 shows a schematic representation of a mixture of eight particles of type B (assumed to be grains of silver halide in a particular case) associated with 40 particles of type A (assumed to be molecules of photographic dye in a particular case). The depiction represents a statistically unlikely situation but conceptually it is simpler than a precise representation of a statistical distribution of a 1:5 stoichiometry of B:A, which would be clustered around the species shown. In some cases it will be desired that the mixture of particles have a distribution as shown in FIG. 2, in which there are still 8 B's and 40 A's. However, although the gross stoichiometry is BA.sub.5 the distribution is no longer clustered around 5 A's per B; the distribution is bimodal, comprising half BA.sub.10 and half B. Consider then a situation in which the desired distribution is to be polymodal. Simple mixing of the two components will not achieve the desired distribution. Individually reacting each stoichiometry for each mode and then mixing the individual batches could be used to furnish repeat batches of non-uniform or polymodal distributions but this is complex and time-consuming. It requires multiple runs with cleanup between each run or multiple reactors at considerable expense. There is thus a need for a simplified method and apparatus to reproducibly furnish non-uniform distributions of polymolecular association clusters.